LTE (Long Term Evolution) has been becoming widespread in place of third generation mobile communication systems (3G: 3rd Generation) as a normalization standard for communication systems. LTE is a communication standard that supports only packet communication, and voices are converted to packets according to VoIP (Voice over Internet Protocol) and then transmitted and received. Particularly, VoIP according to the LTE standard is called VoLTE (Voice over LTE).
With a mobile body communication system, a home base station (femto cell (Femto Cell) base station) is installed to relay communication between a mobile unit(s) and a macro cell base station in order to secure communication quality inside buildings. Conventionally, fixed lines are used for communication from the home base station to a core network including the macro cell base station (for example, see PTL 1).